Pedicle damage. He's had his antlers broken off at the skull and the scar tissue from healing closed off the capillaries that supply the nutrients for building new antler. It's not genetic and he's not sick. Lots of folks assume it's bad genetics because they see bucks with one or no antlers or malformed antlers, but that's not true. It's just old injury.
Here's one on my place still doing buck things, rubbing a tree, hitting scrapes. Not a young guy either. He used to have antlers but a few years ago there was a rash of young yearling & 2yr old bucks that destroyed one another. Every buck on the place had broken tines, beams, even entire antlers broken off at the skull. I knew I'd be seeing some weird stuff in following years and sure enough here's this guy. It happens.
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